Suspended sediment transport on a temperate, microtidal mudflat, the Danish Wadden Sea

Time series measurements of suspended sediment transport and bed level chan ge on a microtidal mudflat of the Danish Wadden Sea were carried out betwee n February 1997 and September 2000, The data show that the mudflat is gener ally accreting except for periods with onshore winds when wave-induced eros ion rakes place during periods of low water levels at the site. In general, a continuous net input of mud was recorded during periods of weak or offsh ore winds. i.e. the import is not event controlled, and this was interrupte d by episodic loss of mud during a few tidal periods with onshore winds. Th e net landward transport of suspended sediment during calm weather or perio ds of offshore wind is caused by settling and seour lag and tidal asymmetry . A very large input of suspended material was observed in the period follo wing a strong storm, the landward directed net transport during the five ti dal periods following the storm being equivalent to approximately 40% of th e net annual accumulation in the area. The typical depth of sediment reworking at the intertidal study site is 2-5 cm. Some seasonal variation can be deduced from the data set with a tenden cy for deposition during spring and summer and erosion in the winter period . The seasonality was especially clear at the most landward station where a ccretion following periods of ice-formation in the area is due to grounding of sediment transported by ice-flees but otherwise deposition is mainly ta king place in the warmer seasons. Net accretion over the three-year measuri ng period along the transect varies between 0.6 and 1.9 cm a (1). Depositio n is largest at the most landward station and the accretion found on the ba sis of repeated bed level measurements compares well with Pb-210 and Cs-137 dating. (C) 2001 Elsevier Science B.V. All rights reserved.